Fluid Structure Interaction (FSI)

Fluid-structure interaction refers to the analyses involving simultaneous fluid flow and solid deformation. Depending on the problem the interaction may be along a shared boundary or internal to the structure —as in the case of poroelasticity. In addition to the solid and fluid deformation, FSI requires handling a moving mesh.

Veryst Engineering has worked on a wide range of FSI problems of different complexities. FSI problems may involve sources of nonlinearity in the solid part (large deformations, contact or nonlinear materials), or the fluid part (turbulence, non-Newtonian fluid properties, or multiphase flow). There could also be additional complexity in solver selection since the ideal solvers for structural and fluid equations are different. The degree of coupling between the fluid and solid fields may be weak or strong, which also affects the solver selection. Finally, mesh movement may be a source of complexity for problems with contact or large deformations, such as shown in the figure below.

FSI problems frequently involve coupling to other physics fields such as heat transfer or electromagnetics. The figure below shows an electrostatic-fluid-structure interaction analysis of a MEMS switch in an enclosed space, surrounded by air. The electrostatic force between beam and ground was calculated directly from the Maxwell stress tensor and accounts for fringe effects.

For some FSI problems we use our engineering judgement to create non-standard FSI models that reduce complexity and solution time. The example below involves the stretching of a fluid-filled tube. We completely removed the fluid part of the model and replaced it by a volumetric constraint when the fluid is a liquid, or a pressure-volume relationship when it is a gas. The reduced model was significantly faster than the full FSI model and the two models predicted very similar results for cases where inertia effects were negligible.

Stretching of fluid-filled tube

Peristaltic Pump Example

Peristaltic pumps move fluid by squeezing an elastomeric tube causing the fluid inside the tube to follow the motion of the roller. Veryst developed FSI models that capture the deformation of the tube, rollers and fluid, the fluid-structure interaction, and contact interaction between the rollers and the hose.

We used the models to investigate the effect of pump design variations such as tube occlusion, tube diameter, and roller speed, on the flow rate, flow fluctuations, and stress state on the tube, thereby improving pump performance.